It is common practice in machines such as power presses to provide lubricated wear plates for reducing the sliding friction between reciprocating machine members in surface engagement with each other. A typical installation in a press, for example, includes a wear plate provided with a solid lubricant mounted on each post of the movable platen and a plain steel wear plate mounted in face-to-face opposition on the stationary post of the fixed platen. The lateral thrust forces resulting from die closure are transmitted by the wear plates on the posts of the movable platen to the wear plates on the posts of the fixed platen. Extremely large lateral thrust forces may be transmitted between mating wear plates during sliding contact therebetween. There is a need for a self-lubricated wear plate capable of operating in the rugged environment of power presses and the like with a high load capacity and a high degree of durability. Reliability and long life are especially important in view of the high cost of down-time in the use of power presses and the like. Further, there is a demand for such self-lubricated wear plates which can be supplied at relatively low cost.
It is well known to provide wear plates with a solid lubricant, such as graphite or molybdenum disulfide, embedded in a metallic wear plate body. In certain applications, it is desirable to provide equal lubricity for sliding friction across the wear plate surface in either of two directions which are mutually perpendicular. This allows the mounting of the wear plate in either of two orientations for reciprocating motion.
In the prior art, it is a common practice to construct wear plates of flat metal bodies defining multiple circular cavities in the surface thereof with "inserts" solid lubricant embedded in the cavities. In a wear plate of this construction, the solid lubricant inserts must be relatively thick in order to withstand the loading on the wear plate without breakage. Typically, the lubricating inserts are formed as plugs with a thickness of about three-eighths inches and a diameter of about three-eighths inches. Wear plates using such plugs are relatively costly to manufacture.
In the prior art, the Nakamura U.S. Pat. No. 4,096,075 granted June 20, 1978 discloses a self-lubricated body with circular inserts of solid lubricant embedded in circular cavities in the surface of the body. In the construction described in this patent, the circular cavities are disposed in a pattern with a predetermined relationship of the distance between cavities and the diameter of the cavities with the cavities being arranged in rows extending at the certain angle. This arrangement is supposed to provide good lubricity in a predetermined direction as well as a direction normal thereto.
A general object of this invention is to provide an improved self-lubricated wear plate which exhibits equal lubricity in either of two mutually perpendicular directions.